One night, when Kozue Kato realizes she’s forgotten some paperwork at her university, she decides to make a late-night trip to grab it.
However, when large dark beasts appear during her errand, she barely escapes with her life thanks to the help of a mysterious woman named Sayuri Shirasagi.
Not all is well, though. Soon reports of people going missing begin to spread. Kozue and Sayuri suspect the creatures and disappearances are related, and they decide to team up to investigate.